The mechanism of biosynthesis, turnover and regulation of the enzymes involved in urea biosynthesis. The mechanism by which thyroxine serves as an inducer of these enzymes in liver of premetamorphic tadpoles, in vivo and in vitro. The factor(s) involved in the concerted regulation of the biosynthesis and degradation of the mitochondrial enzymes carbamyl phosphate synthetase and ornithine transcarbamylase, and of the extramitochondrial enzymes argininosuccinate synthetase, argininosuccinase and arginase. The nature, characterization and role of the thyroxine-binding protein in tadpole liver cytosol and transport of thyroxine to the nucleus. The characterization of the subunits of tadpole liver DNA-dependent RNA polymerases. The active site and mechanism of action of ornithine transcarbamylase. Changes in enzymes and other constituents of liver cell organelles during natural and thyroxine-induced metamorphosis.